#include <assert.h>
#include <stdlib.h> /* for exit */
#include <string.h> /* for strlen */
#include <stdio.h> /* for fprintf etc */
#include "header.h"

/* prototypes */

static void generate(struct generator * g, struct node * p);
static void w(struct generator * g, const char * s);
static void writef(struct generator * g, const char * s, struct node * p);

static int new_label(struct generator * g) {
    return g->next_label++;
}

static struct str * vars_newname(struct generator * g) {
    struct str * output;
    g->var_number++;
    output = str_new();
    str_append_string(output, "v_");
    str_append_int(output, g->var_number);
    return output;
}

/* Write routines for items from the syntax tree */

static void write_varname(struct generator * g, struct name * p) {
    if (p->type != t_external) {
        // We use the same naming scheme for both global and local variables.
        write_char(g, "SBIrxg"[p->type]);
        write_char(g, '_');
    }
    write_s(g, p->s);
}

static void write_varref(struct generator * g, struct name * p) {
    if (p->type != t_grouping && p->local_to == NULL) {
        w(g, "this.#");
    }
    write_varname(g, p);
}

static void write_literal_string(struct generator * g, symbol * p) {
    write_char(g, '"');
    for (int i = 0; i < SIZE(p); i++) {
        int ch = p[i];
        if (32 <= ch && ch < 127) {
            if (ch == '\"' || ch == '\\') write_string(g, "\\");
            write_char(g, ch);
        } else {
            write_string(g, "\\u");
            write_hex4(g, ch);
        }
    }
    write_char(g, '"');
}

static void write_margin(struct generator * g) {
    for (int i = 0; i < g->margin; i++) write_string(g, "    ");
}

static void write_relop(struct generator * g, int relop) {
    // Relational operators are the same as C, save for (in-)equality.
    switch (relop) {
        case c_eq: write_string(g, " === "); break;
        case c_ne: write_string(g, " !== "); break;
        default: write_c_relop(g, relop);
    }
}

static void write_comment(struct generator * g, struct node * p) {
    if (!g->options->comments) return;
    write_margin(g);
    write_string(g, "// ");
    write_comment_content(g, p, NULL);
    write_newline(g);
}

static void write_block_start(struct generator * g) {
    w(g, "~M{~+~N");
}

static void write_block_end(struct generator * g) {
    w(g, "~-~M}~N");
}

static void write_savecursor(struct generator * g, struct node * p,
                             struct str * savevar) {
    g->B[0] = str_data(savevar);
    g->S[1] = "";
    if (p->mode != m_forward) g->S[1] = "this.limit - ";
    writef(g, "~Mconst /** number */ ~B0 = ~S1this.cursor;~N", p);
}

static void append_restore_string(struct node * p, struct str * out, struct str * savevar) {
    str_append_string(out, "this.cursor = ");
    if (p->mode != m_forward) str_append_string(out, "this.limit - ");
    str_append(out, savevar);
    str_append_string(out, ";");
}

static void write_restorecursor(struct generator * g, struct node * p, struct str * savevar) {
    write_margin(g);
    append_restore_string(p, g->outbuf, savevar);
    write_newline(g);
}

static void write_inc_cursor(struct generator * g, struct node * p) {
    write_margin(g);
    write_string(g, p->mode == m_forward ? "this.cursor++;" : "this.cursor--;");
    write_newline(g);
}

static void wsetlab_begin(struct generator * g, int n) {
    g->I[0] = n;
    // This label may end up unused, but we can't easily tell at this point.
    w(g, "~M// deno-lint-ignore no-unused-labels~N");
    w(g, "~Mlab~I0: {~N~+");
}

static void wsetlab_end(struct generator * g) {
    w(g, "~-~M}~N");
}

static void wgotol(struct generator * g, int n) {
    write_margin(g);
    write_string(g, "break lab");
    write_int(g, n);
    write_string(g, ";");
    write_newline(g);
    g->unreachable = true;
}

static void write_failure_(struct generator * g, byte after_if) {
    if (!after_if) write_margin(g);
    if (str_len(g->failure_str) != 0) {
        if (after_if) w(g, "{~N~+~M");
        write_str(g, g->failure_str);
        write_newline(g);
        write_margin(g);
    }
    switch (g->failure_label) {
        case x_return:
            write_string(g, "return false;");
            g->unreachable = true;
            break;
        default:
            write_string(g, "break lab");
            write_int(g, g->failure_label);
            write_string(g, ";");
            g->unreachable = true;
    }
    write_newline(g);
    if (after_if && str_len(g->failure_str) != 0) {
        w(g, "~-~M}~N");
    }
}

static void write_failure(struct generator * g) {
    write_failure_(g, false);
}

static void write_failure_after_if(struct generator * g) {
    write_failure_(g, true);
}

static void write_failure_if(struct generator * g, const char * s, struct node * p) {
    writef(g, "~Mif (", p);
    writef(g, s, p);
    writef(g, ") ", p);
    write_failure_after_if(g);
    g->unreachable = false;
}

/* if at limit fail */
static void write_check_limit(struct generator * g, struct node * p) {
    if (p->mode == m_forward) {
        write_failure_if(g, "this.cursor >= this.limit", p);
    } else {
        write_failure_if(g, "this.cursor <= this.limit_backward", p);
    }
}

/* Formatted write. */
static void writef(struct generator * g, const char * input, struct node * p) {
    (void)p;
    int i = 0;

    while (input[i]) {
        int ch = input[i++];
        if (ch != '~') {
            write_char(g, ch);
            continue;
        }
        ch = input[i++];
        switch (ch) {
            case '~': write_char(g, '~'); continue;
            case 'f': write_failure(g);
                      g->unreachable = false;
                      continue;
            case 'M': write_margin(g); continue;
            case 'N': write_newline(g); continue;
            case '{': write_block_start(g); continue;
            case '}': write_block_end(g); continue;
            case 'S': {
                int j = input[i++] - '0';
                if (j < 0 || j > (int)(sizeof(g->S) / sizeof(g->S[0]))) {
                    printf("Invalid escape sequence ~%c%c in writef(g, \"%s\", p)\n",
                           ch, input[i - 1], input);
                    exit(1);
                }
                write_string(g, g->S[j]);
                continue;
            }
            case 'B': {
                int j = input[i++] - '0';
                if (j < 0 || j > (int)(sizeof(g->B) / sizeof(g->B[0])))
                    goto invalid_escape2;
                write_s(g, g->B[j]);
                continue;
            }
            case 'F': { // Among function dispatcher.
                struct among * x = p->among;
                if (x->function_count == 0) {
                    continue;
                }

                w(g, ", ");

                if (x->function_count == 1) {
                    // Only one different function used in this among.
                    struct amongvec * v = x->b;
                    for (int j = 0; j < x->literalstring_count; j++) {
                        if (v[j].function) {
                            write_varref(g, v[j].function);
                            goto continue_outer_loop;
                        }
                    }
                    fprintf(stderr, "function_count == 1 but no among functions\n");
                    exit(1);
continue_outer_loop:
                    continue;
                }

                w(g, "this.#af_");
                write_int(g, x->number);
                continue;
            }
            case 'I': {
                int j = input[i++] - '0';
                if (j < 0 || j > (int)(sizeof(g->I) / sizeof(g->I[0])))
                    goto invalid_escape2;
                write_int(g, g->I[j]);
                continue;
            }
            case 'V':
                write_varref(g, p->name);
                continue;
            case 'W':
                write_varname(g, p->name);
                continue;
            case 'L':
                write_literal_string(g, p->literalstring);
                continue;
            case '+': g->margin++; continue;
            case '-': g->margin--; continue;
            case 'n': write_s(g, g->options->name); continue;
            case 'P': write_string(g, g->options->parent_class_name); continue;
            default:
                printf("Invalid escape sequence ~%c in writef(g, \"%s\", p)\n",
                       ch, input);
                exit(1);
            invalid_escape2:
                printf("Invalid escape sequence ~%c%c in writef(g, \"%s\", p)\n",
                       ch, input[i - 1], input);
                exit(1);
        }
    }
}

static void w(struct generator * g, const char * s) {
    writef(g, s, NULL);
}

static void generate_AE(struct generator * g, struct node * p) {
    const char * s;
    switch (p->type) {
        case c_name:
            write_varref(g, p->name); break;
        case c_number:
            write_int(g, p->number); break;
        case c_maxint:
            write_string(g, "(-1>>>1)"); break;
        case c_minint:
            write_string(g, "(~(-1>>>1))"); break;
        case c_neg:
            write_char(g, '-'); generate_AE(g, p->right); break;
        case c_multiply:
            s = " * "; goto label0;
        case c_plus:
            s = " + "; goto label0;
        case c_minus:
            s = " - ";
        label0:
            write_char(g, '('); generate_AE(g, p->left);
            write_string(g, s); generate_AE(g, p->right); write_char(g, ')'); break;
        case c_divide:
            /* Snowball specifies integer division with semantics matching C,
             * so we need to use `Math.trunc(x/y)` here.
             */
            write_string(g, "Math.trunc(");
            generate_AE(g, p->left);
            write_string(g, " / ");
            generate_AE(g, p->right);
            write_char(g, ')');
            break;
        case c_cursor:
            w(g, "this.cursor"); break;
        case c_limit:
            w(g, p->mode == m_forward ? "this.limit" : "this.limit_backward"); break;
        case c_lenof: /* Same as sizeof() for Javascript. */
        case c_sizeof:
            writef(g, "~V.length", p);
            break;
        case c_len: /* Same as size() for Javascript. */
        case c_size:
            w(g, "this.current.length");
            break;
    }
}

static void generate_bra(struct generator * g, struct node * p) {
    write_comment(g, p);
    p = p->left;
    while (p) {
        generate(g, p);
        p = p->right;
    }
}

static void generate_and(struct generator * g, struct node * p) {
    struct str * savevar = NULL;
    if (K_needed(g, p->left)) {
        savevar = vars_newname(g);
    }

    write_comment(g, p);

    if (savevar) write_savecursor(g, p, savevar);

    p = p->left;
    while (p) {
        generate(g, p);
        if (g->unreachable) break;
        if (savevar && p->right != NULL) write_restorecursor(g, p, savevar);
        p = p->right;
    }

    if (savevar) {
        str_delete(savevar);
    }
}

static void generate_or(struct generator * g, struct node * p) {
    struct str * savevar = NULL;
    if (K_needed(g, p->left)) {
        savevar = vars_newname(g);
    }

    int a0 = g->failure_label;
    struct str * a1 = str_copy(g->failure_str);

    int out_lab = new_label(g);
    int end_unreachable = true;

    write_comment(g, p);
    wsetlab_begin(g, out_lab);

    if (savevar) write_savecursor(g, p, savevar);

    p = p->left;
    str_clear(g->failure_str);

    if (p == NULL) {
        /* p should never be NULL after an or: there should be at least two
         * sub nodes. */
        fprintf(stderr, "Error: \"or\" node without children nodes.");
        exit(1);
    }
    while (p->right != NULL) {
        g->failure_label = new_label(g);
        wsetlab_begin(g, g->failure_label);
        generate(g, p);
        if (!g->unreachable) {
            wgotol(g, out_lab);
            end_unreachable = false;
        }
        wsetlab_end(g);
        g->unreachable = false;
        if (savevar) write_restorecursor(g, p, savevar);
        p = p->right;
    }

    g->failure_label = a0;
    str_delete(g->failure_str);
    g->failure_str = a1;

    generate(g, p);
    wsetlab_end(g);
    if (!end_unreachable) {
        g->unreachable = false;
    }

    if (savevar) {
        str_delete(savevar);
    }
}

static void generate_backwards(struct generator * g, struct node * p) {
    write_comment(g, p);
    writef(g, "~Mthis.limit_backward = this.cursor; this.cursor = this.limit;~N", p);
    generate(g, p->left);
    w(g, "~Mthis.cursor = this.limit_backward;~N");
}


static void generate_not(struct generator * g, struct node * p) {
    struct str * savevar = NULL;
    if (K_needed(g, p->left)) {
        savevar = vars_newname(g);
    }

    int a0 = g->failure_label;
    struct str * a1 = str_copy(g->failure_str);

    write_comment(g, p);
    if (savevar) {
        write_block_start(g);
        write_savecursor(g, p, savevar);
    }

    g->failure_label = new_label(g);
    str_clear(g->failure_str);

    wsetlab_begin(g, g->failure_label);

    generate(g, p->left);

    g->failure_label = a0;
    str_delete(g->failure_str);
    g->failure_str = a1;

    if (!g->unreachable) write_failure(g);

    wsetlab_end(g);
    g->unreachable = false;

    if (savevar) {
        write_restorecursor(g, p, savevar);
        write_block_end(g);
        str_delete(savevar);
    }
}


static void generate_try(struct generator * g, struct node * p) {
    struct str * savevar = NULL;
    if (K_needed(g, p->left)) {
        savevar = vars_newname(g);
    }

    g->failure_label = new_label(g);
    str_clear(g->failure_str);

    write_comment(g, p);
    if (savevar) {
        write_savecursor(g, p, savevar);
        append_restore_string(p, g->failure_str, savevar);
    }

    wsetlab_begin(g, g->failure_label);
    generate(g, p->left);
    wsetlab_end(g);
    g->unreachable = false;

    if (savevar) {
        str_delete(savevar);
    }
}

static void generate_set(struct generator * g, struct node * p) {
    write_comment(g, p);
    writef(g, "~M~V = true;~N", p);
}

static void generate_unset(struct generator * g, struct node * p) {
    write_comment(g, p);
    writef(g, "~M~V = false;~N", p);
}

static void generate_fail(struct generator * g, struct node * p) {
    write_comment(g, p);
    generate(g, p->left);
    if (!g->unreachable) write_failure(g);
}

/* generate_test() also implements 'reverse' */

static void generate_test(struct generator * g, struct node * p) {
    struct str * savevar = NULL;
    if (K_needed(g, p->left)) {
        savevar = vars_newname(g);
    }

    write_comment(g, p);

    if (savevar) {
        write_savecursor(g, p, savevar);
    }

    generate(g, p->left);

    if (savevar) {
        if (!g->unreachable) {
            write_restorecursor(g, p, savevar);
        }
        str_delete(savevar);
    }
}

static void generate_do(struct generator * g, struct node * p) {
    struct str * savevar = NULL;
    if (K_needed(g, p->left)) {
        savevar = vars_newname(g);
    }

    write_comment(g, p);
    if (savevar) write_savecursor(g, p, savevar);

    if (p->left->type == c_call) {
        /* Optimise do <call> */
        write_comment(g, p->left);
        writef(g, "~M~V();~N", p->left);
    } else {
        g->failure_label = new_label(g);
        str_clear(g->failure_str);

        wsetlab_begin(g, g->failure_label);
        generate(g, p->left);
        wsetlab_end(g);
        g->unreachable = false;
    }

    if (savevar) {
        write_restorecursor(g, p, savevar);
        str_delete(savevar);
    }
}

static void generate_next(struct generator * g, struct node * p) {
    write_comment(g, p);
    write_check_limit(g, p);
    write_inc_cursor(g, p);
}

static void generate_GO_grouping(struct generator * g, struct node * p, int is_goto, int complement) {
    write_comment(g, p);

    struct grouping * q = p->name->grouping;
    g->S[0] = p->mode == m_forward ? "" : "_b";
    g->S[1] = complement ? "in" : "out";
    g->I[0] = q->smallest_ch;
    g->I[1] = q->largest_ch;
    write_failure_if(g, "!this.go_~S1_grouping~S0(~V, ~I0, ~I1)", p);
    if (!is_goto) {
        if (p->mode == m_forward)
            w(g, "~Mthis.cursor++;~N");
        else
            w(g, "~Mthis.cursor--;~N");
    }
}

static void generate_GO(struct generator * g, struct node * p, int style) {
    write_comment(g, p);

    int a0 = g->failure_label;
    struct str * a1 = str_copy(g->failure_str);

    int end_unreachable = false;
    int golab = new_label(g);
    g->I[0] = golab;
    // This label may end up unused, but we can't easily tell at this point.
    w(g, "~M// deno-lint-ignore no-unused-labels~N");
    w(g, "~Mgolab~I0: while (true)~N");
    w(g, "~{");

    struct str * savevar = NULL;
    if (style == 1 || repeat_restore(g, p->left)) {
        savevar = vars_newname(g);
        write_savecursor(g, p, savevar);
    }

    g->failure_label = new_label(g);
    str_clear(g->failure_str);
    wsetlab_begin(g, g->failure_label);
    generate(g, p->left);

    if (g->unreachable) {
        /* Cannot break out of this loop: therefore the code after the
         * end of the loop is unreachable.*/
        end_unreachable = true;
    } else {
        /* include for goto; omit for gopast */
        if (style == 1) write_restorecursor(g, p, savevar);
        g->I[0] = golab;
        w(g, "~Mbreak golab~I0;~N");
    }
    g->unreachable = false;
    wsetlab_end(g);
    if (savevar) {
        write_restorecursor(g, p, savevar);
        str_delete(savevar);
    }

    g->failure_label = a0;
    str_delete(g->failure_str);
    g->failure_str = a1;

    write_check_limit(g, p);
    write_inc_cursor(g, p);
    write_block_end(g);
    g->unreachable = end_unreachable;
}

static void generate_loop(struct generator * g, struct node * p) {
    struct str * loopvar = vars_newname(g);
    write_comment(g, p);
    g->B[0] = str_data(loopvar);
    w(g, "~Mfor (let /** number */ ~B0 = ");
    generate_AE(g, p->AE);
    g->B[0] = str_data(loopvar);
    writef(g, "; ~B0 > 0; ~B0--)~N", p);
    writef(g, "~{", p);

    generate(g, p->left);

    w(g, "~}");
    str_delete(loopvar);
    g->unreachable = false;
}

static void generate_repeat_or_atleast(struct generator * g, struct node * p, struct str * loopvar) {
    writef(g, "~Mwhile (true) {~N~+", p);

    struct str * savevar = NULL;
    if (repeat_restore(g, p->left)) {
        savevar = vars_newname(g);
        write_savecursor(g, p, savevar);
    }

    g->failure_label = new_label(g);
    str_clear(g->failure_str);
    wsetlab_begin(g, g->failure_label);
    generate(g, p->left);

    if (!g->unreachable) {
        if (loopvar != NULL) {
            g->B[0] = str_data(loopvar);
            w(g, "~M~B0--;~N");
        }

        w(g, "~Mcontinue;~N");
    }

    wsetlab_end(g);
    g->unreachable = false;

    if (savevar) {
        write_restorecursor(g, p, savevar);
        str_delete(savevar);
    }

    w(g, "~Mbreak;~N~}");
}

static void generate_repeat(struct generator * g, struct node * p) {
    write_comment(g, p);
    generate_repeat_or_atleast(g, p, NULL);
}

static void generate_atleast(struct generator * g, struct node * p) {
    struct str * loopvar = vars_newname(g);

    write_comment(g, p);
    w(g, "~{");
    g->B[0] = str_data(loopvar);
    w(g, "~Mlet ~B0 = ");
    generate_AE(g, p->AE);
    w(g, ";~N");
    {
        int a0 = g->failure_label;
        struct str * a1 = str_copy(g->failure_str);

        generate_repeat_or_atleast(g, p, loopvar);

        g->failure_label = a0;
        str_delete(g->failure_str);
        g->failure_str = a1;
    }
    g->B[0] = str_data(loopvar);
    write_failure_if(g, "~B0 > 0", p);
    w(g, "~}");
    str_delete(loopvar);
}

static void generate_setmark(struct generator * g, struct node * p) {
    write_comment(g, p);
    writef(g, "~M~V = this.cursor;~N", p);
}

static void generate_tomark(struct generator * g, struct node * p) {
    write_comment(g, p);
    g->S[0] = p->mode == m_forward ? ">" : "<";

    w(g, "~Mif (this.cursor ~S0 "); generate_AE(g, p->AE); w(g, ") ");
    write_failure_after_if(g);
    g->unreachable = false;
    w(g, "~Mthis.cursor = "); generate_AE(g, p->AE); writef(g, ";~N", p);
}

static void generate_atmark(struct generator * g, struct node * p) {
    write_comment(g, p);
    w(g, "~Mif (this.cursor !== "); generate_AE(g, p->AE); writef(g, ") ", p);
    write_failure_after_if(g);
    g->unreachable = false;
}

static void generate_hop(struct generator * g, struct node * p) {
    write_comment(g, p);
    g->S[0] = p->mode == m_forward ? "+" : "-";

    w(g, "~{~Mconst /** number */ c = this.cursor ~S0 ");
    generate_AE(g, p->AE);
    w(g, ";~N");

    g->S[1] = p->mode == m_forward ? "> this.limit" : "< this.limit_backward";
    g->S[2] = p->mode == m_forward ? "<" : ">";
    if (p->AE->type == c_number) {
        // Constant distance hop.
        //
        // No need to check for negative hop as that's converted to false by
        // the analyser.
        write_failure_if(g, "c ~S1", p);
    } else {
        write_failure_if(g, "c ~S1 || c ~S2 this.cursor", p);
    }
    writef(g, "~Mthis.cursor = c;~N", p);
    writef(g, "~}", p);
}

static void generate_delete(struct generator * g, struct node * p) {
    write_comment(g, p);
    writef(g, "~Mthis.slice_del();~N", p);
}

static void generate_tolimit(struct generator * g, struct node * p) {
    write_comment(g, p);
    if (p->mode == m_forward) {
        writef(g, "~Mthis.cursor = this.limit;~N", p);
    } else {
        writef(g, "~Mthis.cursor = this.limit_backward;~N", p);
    }
}

static void generate_atlimit(struct generator * g, struct node * p) {
    write_comment(g, p);
    if (p->mode == m_forward) {
        write_failure_if(g, "this.cursor < this.limit", p);
    } else {
        write_failure_if(g, "this.cursor > this.limit_backward", p);
    }
}

static void generate_leftslice(struct generator * g, struct node * p) {
    write_comment(g, p);
    if (p->mode == m_forward) {
        writef(g, "~Mthis.bra = this.cursor;~N", p);
    } else {
        writef(g, "~Mthis.ket = this.cursor;~N", p);
    }
}

static void generate_rightslice(struct generator * g, struct node * p) {
    write_comment(g, p);
    if (p->mode == m_forward) {
        writef(g, "~Mthis.ket = this.cursor;~N", p);
    } else {
        writef(g, "~Mthis.bra = this.cursor;~N", p);
    }
}

static void generate_assignto(struct generator * g, struct node * p) {
    write_comment(g, p);
    writef(g, "~M~V = this.current.slice(0, this.limit);~N", p);
}

static void generate_sliceto(struct generator * g, struct node * p) {
    write_comment(g, p);
    writef(g, "~M~V = this.slice_to();~N", p);
}

static void generate_address(struct generator * g, struct node * p) {
    symbol * b = p->literalstring;
    if (b != NULL) {
        write_literal_string(g, b);
    } else {
        write_varref(g, p->name);
    }
}

static void generate_insert(struct generator * g, struct node * p, int style) {

    int keep_c = style == c_attach;
    write_comment(g, p);
    if (p->mode == m_backward) keep_c = !keep_c;
    if (keep_c) {
        w(g, "~{~Mconst /** number */ c = this.cursor;~N");
        writef(g, "~Mthis.insert(c, c, ", p);
    } else {
        writef(g, "~Mthis.insert(this.cursor, this.cursor, ", p);
    }
    generate_address(g, p);
    writef(g, ");~N", p);
    if (keep_c) w(g, "~Mthis.cursor = c;~N~}");
}

static void generate_assignfrom(struct generator * g, struct node * p) {

    int keep_c = p->mode == m_forward; /* like 'attach' */

    write_comment(g, p);
    if (keep_c) {
        w(g, "~{~Mconst /** number */ c = this.cursor;~N");
        if (p->mode == m_forward) {
            writef(g, "~Mthis.insert(c, this.limit, ", p);
        } else {
            writef(g, "~Mthis.insert(this.limit_backward, c, ", p);
        }
    } else {
        if (p->mode == m_forward) {
            writef(g, "~Mthis.insert(this.cursor, this.limit, ", p);
        } else {
            writef(g, "~Mthis.insert(this.limit_backward, this.cursor, ", p);
        }
    }
    generate_address(g, p);
    writef(g, ");~N", p);
    if (keep_c) w(g, "~Mthis.cursor = c;~N~}");
}

static void generate_slicefrom(struct generator * g, struct node * p) {
    write_comment(g, p);
    w(g, "~Mthis.slice_from(");
    generate_address(g, p);
    writef(g, ");~N", p);
}

static void generate_setlimit(struct generator * g, struct node * p) {
    struct str * varname = vars_newname(g);
    write_comment(g, p);
    if (p->left && p->left->type == c_tomark) {
        /* Special case for:
         *
         *   setlimit tomark AE for C
         *
         * All uses of setlimit in the current stemmers we ship follow this
         * pattern, and by special-casing we can avoid having to save and
         * restore c.
         */
        struct node * q = p->left;
        write_comment(g, q);
        g->S[0] = q->mode == m_forward ? ">" : "<";
        w(g, "~Mif (this.cursor ~S0 "); generate_AE(g, q->AE); w(g, ") ");
        write_failure_after_if(g);
        g->unreachable = false;

        g->B[0] = str_data(varname);
        w(g, "~Mconst /** number */ ~B0 = ");
        if (p->mode == m_forward) {
            w(g, "this.limit - this.cursor;~N");
            w(g, "~Mthis.limit = ");
        } else {
            w(g, "this.limit_backward;~N");
            w(g, "~Mthis.limit_backward = ");
        }
        generate_AE(g, q->AE); writef(g, ";~N", q);

        if (p->mode == m_forward) {
            str_assign(g->failure_str, "this.limit += ");
            str_append(g->failure_str, varname);
            str_append_ch(g->failure_str, ';');
        } else {
            str_assign(g->failure_str, "this.limit_backward = ");
            str_append(g->failure_str, varname);
            str_append_ch(g->failure_str, ';');
        }
    } else {
        struct str * savevar = vars_newname(g);
        write_savecursor(g, p, savevar);

        generate(g, p->left);

        if (!g->unreachable) {
            g->B[0] = str_data(varname);
            w(g, "~Mconst /** number */ ~B0 = ");
            if (p->mode == m_forward) {
                w(g, "this.limit - this.cursor;~N");
                w(g, "~Mthis.limit = this.cursor;~N");
            } else {
                w(g, "this.limit_backward;~N");
                w(g, "~Mthis.limit_backward = this.cursor;~N");
            }
            write_restorecursor(g, p, savevar);

            if (p->mode == m_forward) {
                str_assign(g->failure_str, "this.limit += ");
                str_append(g->failure_str, varname);
                str_append_ch(g->failure_str, ';');
            } else {
                str_assign(g->failure_str, "this.limit_backward = ");
                str_append(g->failure_str, varname);
                str_append_ch(g->failure_str, ';');
            }
        }
        str_delete(savevar);
    }

    if (!g->unreachable) {
        generate(g, p->aux);

        if (!g->unreachable) {
            write_margin(g);
            write_str(g, g->failure_str);
            write_newline(g);
        }
    }
    str_delete(varname);
}

/* dollar sets snowball up to operate on a string variable as if it were the
 * current string */
static void generate_dollar(struct generator * g, struct node * p) {
    write_comment(g, p);

    int a0 = g->failure_label;
    struct str * a1 = str_copy(g->failure_str);
    g->failure_label = new_label(g);
    str_clear(g->failure_str);

    struct str * savevar = vars_newname(g);
    g->B[0] = str_data(savevar);
    writef(g, "~{~N"
              "~Mconst /** !Object */ ~B0 = new ~P();~N", p);
    writef(g, "~M~B0.copy_from(this);~N", p);

    writef(g, "~Mthis.current = ~V;~N"
              "~Mthis.cursor = 0;~N"
              "~Mthis.limit_backward = 0;~N"
              "~Mthis.limit = this.current.length;~N", p);
    if (p->left->possible_signals == -1) {
        /* Assume failure. */
        w(g, "~Mlet /**boolean*/ ~B0_f = true;~N");
    }

    wsetlab_begin(g, g->failure_label);

    generate(g, p->left);

    if (p->left->possible_signals == -1) {
        /* Mark success. */
        g->B[0] = str_data(savevar);
        w(g, "~M~B0_f = false;~N");
    }

    wsetlab_end(g);

    g->failure_label = a0;
    str_delete(g->failure_str);
    g->failure_str = a1;

    g->B[0] = str_data(savevar);
    writef(g, "~M~V = this.current;~N"
              "~Mthis.copy_from(~B0);~N", p);
    ++g->copy_from_count;
    if (p->left->possible_signals == 0) {
        // p->left always signals f.
        write_failure(g);
    } else if (p->left->possible_signals == -1) {
        write_failure_if(g, "~B0_f", p);
    }
    w(g, "~}");

    str_delete(savevar);
}

static void generate_integer_assign(struct generator * g, struct node * p, const char * s) {
    write_comment(g, p);
    if (p->AE->type == c_number && p->AE->number == 1) {
        if (strcmp(s, "+=") == 0) {
            // Optimise `+= 1` to increment.
            writef(g, "~M++~V;~N", p);
            return;
        } else if (strcmp(s, "-=") == 0) {
            // Optimise `-= 1` to decrement.
            writef(g, "~M--~V;~N", p);
            return;
        }
    }
    g->S[0] = s;
    writef(g, "~M~V ~S0 ", p);
    generate_AE(g, p->AE);
    w(g, ";~N");
}

static void generate_integer_test(struct generator * g, struct node * p) {
    write_comment(g, p);
    int relop = p->type;
    int optimise_to_return = tailcallable(g, p);
    if (optimise_to_return) {
        w(g, "~Mreturn ");
        p->right = NULL;
    } else {
        w(g, "~Mif (");
        // We want the inverse of the snowball test here.
        relop ^= 1;
    }
    generate_AE(g, p->left);
    write_relop(g, relop);
    generate_AE(g, p->AE);
    if (optimise_to_return) {
        w(g, ";~N");
    } else {
        w(g, ") ");
        write_failure_after_if(g);
        g->unreachable = false;
    }
}

static void generate_call(struct generator * g, struct node * p) {
    int signals = p->name->definition->possible_signals;
    write_comment(g, p);
    if (tailcallable(g, p)) {
        /* Tail call. */
        writef(g, "~Mreturn ~V();~N", p);
        p->right = NULL;
        g->unreachable = true;
        return;
    }
    if (just_return_on_fail(g) && signals == 0) {
        /* Always fails. */
        writef(g, "~Mreturn ~V();~N", p);
        g->unreachable = true;
        return;
    }
    if (signals == 1) {
        /* Always succeeds. */
        writef(g, "~M~V();~N", p);
    } else if (signals == 0) {
        /* Always fails. */
        writef(g, "~M~V();~N", p);
        write_failure(g);
    } else {
        write_failure_if(g, "!~V()", p);
    }
}

static void generate_grouping(struct generator * g, struct node * p, int complement) {
    write_comment(g, p);

    struct grouping * q = p->name->grouping;
    g->S[0] = p->mode == m_forward ? "" : "_b";
    g->S[1] = complement ? "out" : "in";
    g->I[0] = q->smallest_ch;
    g->I[1] = q->largest_ch;
    if (tailcallable(g, p)) {
        writef(g, "~Mreturn this.~S1_grouping~S0(~V, ~I0, ~I1);~N", p);
        p->right = NULL;
    } else {
        write_failure_if(g, "!(this.~S1_grouping~S0(~V, ~I0, ~I1))", p);
    }
}

static void generate_namedstring(struct generator * g, struct node * p) {
    write_comment(g, p);
    g->S[0] = p->mode == m_forward ? "" : "_b";
    if (tailcallable(g, p)) {
        writef(g, "~Mreturn this.eq_s~S0(~V);~N", p);
        p->right = NULL;
    } else {
        write_failure_if(g, "!(this.eq_s~S0(~V))", p);
    }
}

static void generate_literalstring(struct generator * g, struct node * p) {
    write_comment(g, p);
    g->S[0] = p->mode == m_forward ? "" : "_b";
    if (tailcallable(g, p)) {
        writef(g, "~Mreturn this.eq_s~S0(~L);~N", p);
        p->right = NULL;
    } else {
        write_failure_if(g, "!(this.eq_s~S0(~L))", p);
    }
}

static void generate_define(struct generator * g, struct node * p) {
    struct name * q = p->name;

    write_newline(g);
    write_comment(g, p);

    writef(g, "~M/** @return {boolean} */~N"
              "~M#~W() {~+~N", p);

    /* Save output. */
    struct str * saved_output = g->outbuf;
    struct str * saved_declarations = g->declarations;
    g->outbuf = str_new();
    g->declarations = str_new();

    g->next_label = 0;
    g->var_number = 0;

    /* Declare local variables. */
    for (struct name * name = g->analyser->names; name; name = name->next) {
        if (name->local_to == q) {
            switch (name->type) {
                case t_string:
                    w(g, "~Mlet /** string */ ");
                    write_varname(g, name);
                    w(g, ";~N");
                    break;
                case t_integer:
                    w(g, "~Mlet /** number */ ");
                    write_varname(g, name);
                    w(g, ";~N");
                    break;
                case t_boolean:
                    w(g, "~Mlet /** boolean */ ");
                    write_varname(g, name);
                    w(g, ";~N");
                    break;
            }
        }
    }

    if (q->amongvar_needed) {
        // The "among var" (`a`) is only assigned to, but the initialisation
        // can be generated in a nested block so it seems hard to declare it as
        // const and still have it visible when we want to use it.
        w(g, "~Mlet /** number */ a;~N");
    }
    str_clear(g->failure_str);
    g->failure_label = x_return;
    g->unreachable = false;
    g->keep_count = 0;
    int signals = p->left->possible_signals;

    /* Generate function body. */
    generate(g, p->left);
    if (p->left->right) {
        assert(p->left->right->type == c_functionend);
        if (signals) {
            generate(g, p->left->right);
        }
    }
    w(g, "~-~M}~N");

    if (q->type == t_external) {
        w(g, "~N");
        w(g, "~M/**@return{string}*/~N");
        writef(g, "~M~W(/**string*/input) {~+~N", p);
        w(g, "~Mthis.setCurrent(input);~N");
        writef(g, "~Mthis.#~W();~N", p);
        w(g, "~Mreturn this.getCurrent();~N");
        w(g, "~-~M}~N");

        if (SIZE(q->s) == 4 && memcmp(q->s, "stem", 4) == 0) {
            w(g, "~N");
            w(g, "~MstemWord = this.stem;~N");
        }
    }

    str_append(saved_output, g->declarations);
    str_append(saved_output, g->outbuf);
    str_delete(g->declarations);
    str_delete(g->outbuf);
    g->declarations = saved_declarations;
    g->outbuf = saved_output;
}

static void generate_functionend(struct generator * g, struct node * p) {
    (void)p;
    w(g, "~Mreturn true;~N");
}

static void generate_substring(struct generator * g, struct node * p) {
    write_comment(g, p);

    struct among * x = p->among;

    g->S[0] = p->mode == m_forward ? "" : "_b";
    g->I[0] = x->number;

    if (x->amongvar_needed) {
        writef(g, "~Ma = this.find_among~S0(a_~I0~F);~N", p);
        if (!x->always_matches) {
            write_failure_if(g, "a === 0", p);
        }
    } else if (x->always_matches) {
        writef(g, "~Mthis.find_among~S0(a_~I0~F);~N", p);
    } else if (x->command_count == 0 && tailcallable(g, p)) {
        writef(g, "~Mreturn this.find_among~S0(a_~I0~F) !== 0;~N", p);
        x->node->right = NULL;
        g->unreachable = true;
    } else {
        write_failure_if(g, "this.find_among~S0(a_~I0~F) === 0", p);
    }
}

static void generate_among(struct generator * g, struct node * p) {
    struct among * x = p->among;

    if (x->substring == NULL) {
        generate_substring(g, p);
    } else {
        write_comment(g, p);
    }

    if (x->command_count == 1 && x->nocommand_count == 0) {
        /* Only one outcome ("no match" already handled). */
        generate(g, x->commands[0]);
    } else if (x->command_count > 0) {
        w(g, "~Mswitch (a) {~N~+");
        for (int i = 1; i <= x->command_count; i++) {
            g->I[0] = i;
            w(g, "~Mcase ~I0: {~N~+");
            generate(g, x->commands[i - 1]);
            if (!g->unreachable) w(g, "~Mbreak;~N");
            w(g, "~-~M}~N");
            g->unreachable = false;
        }
        write_block_end(g);
    }
}

static void generate_booltest(struct generator * g, struct node * p, int inverted) {
    write_comment(g, p);
    if (tailcallable(g, p)) {
        // Optimise at end of function.
        if (inverted) {
            writef(g, "~Mreturn !~V;~N", p);
        } else {
            writef(g, "~Mreturn ~V;~N", p);
        }
        p->right = NULL;
        g->unreachable = true;
        return;
    }
    if (inverted) {
        write_failure_if(g, "~V", p);
    } else {
        write_failure_if(g, "!~V", p);
    }
}

static void generate_false(struct generator * g, struct node * p) {
    write_comment(g, p);
    write_failure(g);
}

static void generate_debug(struct generator * g, struct node * p) {
    write_comment(g, p);
    g->I[0] = g->debug_count++;
    g->I[1] = p->line_number;
    writef(g, "~Mthis.debug(~I0, ~I1);~N", p);
}

static void generate(struct generator * g, struct node * p) {
    if (g->unreachable) return;

    int a0 = g->failure_label;
    struct str * a1 = str_copy(g->failure_str);

    switch (p->type) {
        case c_define:        generate_define(g, p); break;
        case c_bra:           generate_bra(g, p); break;
        case c_and:           generate_and(g, p); break;
        case c_or:            generate_or(g, p); break;
        case c_backwards:     generate_backwards(g, p); break;
        case c_not:           generate_not(g, p); break;
        case c_set:           generate_set(g, p); break;
        case c_unset:         generate_unset(g, p); break;
        case c_try:           generate_try(g, p); break;
        case c_fail:          generate_fail(g, p); break;
        case c_reverse:
        case c_test:          generate_test(g, p); break;
        case c_do:            generate_do(g, p); break;
        case c_goto:          generate_GO(g, p, 1); break;
        case c_gopast:        generate_GO(g, p, 0); break;
        case c_goto_grouping: generate_GO_grouping(g, p, 1, 0); break;
        case c_gopast_grouping:
                              generate_GO_grouping(g, p, 0, 0); break;
        case c_goto_non:      generate_GO_grouping(g, p, 1, 1); break;
        case c_gopast_non:    generate_GO_grouping(g, p, 0, 1); break;
        case c_repeat:        generate_repeat(g, p); break;
        case c_loop:          generate_loop(g, p); break;
        case c_atleast:       generate_atleast(g, p); break;
        case c_setmark:       generate_setmark(g, p); break;
        case c_tomark:        generate_tomark(g, p); break;
        case c_atmark:        generate_atmark(g, p); break;
        case c_hop:           generate_hop(g, p); break;
        case c_delete:        generate_delete(g, p); break;
        case c_next:          generate_next(g, p); break;
        case c_tolimit:       generate_tolimit(g, p); break;
        case c_atlimit:       generate_atlimit(g, p); break;
        case c_leftslice:     generate_leftslice(g, p); break;
        case c_rightslice:    generate_rightslice(g, p); break;
        case c_assignto:      generate_assignto(g, p); break;
        case c_sliceto:       generate_sliceto(g, p); break;
        case c_assign:        generate_assignfrom(g, p); break;
        case c_insert:
        case c_attach:        generate_insert(g, p, p->type); break;
        case c_slicefrom:     generate_slicefrom(g, p); break;
        case c_setlimit:      generate_setlimit(g, p); break;
        case c_dollar:        generate_dollar(g, p); break;
        case c_mathassign:    generate_integer_assign(g, p, "="); break;
        case c_plusassign:    generate_integer_assign(g, p, "+="); break;
        case c_minusassign:   generate_integer_assign(g, p, "-="); break;
        case c_multiplyassign:generate_integer_assign(g, p, "*="); break;
        case c_divideassign:
            /* Snowball specifies integer division with semantics matching C,
             * so we need to use `Math.trunc(x/y)` here.
             */
            writef(g, "~M~V = Math.trunc(~V / ", p);
            generate_AE(g, p->AE);
            w(g, ");~N");
            break;
        case c_eq:
        case c_ne:
        case c_gt:
        case c_ge:
        case c_lt:
        case c_le:
            generate_integer_test(g, p);
            break;
        case c_call:          generate_call(g, p); break;
        case c_grouping:      generate_grouping(g, p, false); break;
        case c_non:           generate_grouping(g, p, true); break;
        case c_name:          generate_namedstring(g, p); break;
        case c_literalstring: generate_literalstring(g, p); break;
        case c_among:         generate_among(g, p); break;
        case c_substring:     generate_substring(g, p); break;
        case c_booltest:      generate_booltest(g, p, false); break;
        case c_not_booltest:  generate_booltest(g, p, true); break;
        case c_false:         generate_false(g, p); break;
        case c_true:          break;
        case c_debug:         generate_debug(g, p); break;
        case c_functionend:   generate_functionend(g, p); break;
        default: fprintf(stderr, "%d encountered\n", p->type);
                 exit(1);
    }

    g->failure_label = a0;
    str_delete(g->failure_str);
    g->failure_str = a1;
}

static void generate_class_begin(struct generator * g) {
    w(g, "import { ~P } from './base-stemmer.js'~N"
         "~N"
         "class ~n extends ~P {~+~N");
    write_newline(g);
}

static void generate_class_end(struct generator * g) {
    w(g, "~-}~N");
    w(g, "~N");
    w(g, "export { ~n };~N");
}

static void generate_among_table(struct generator * g, struct among * x) {
    write_comment(g, x->node);

    struct amongvec * v = x->b;

    g->I[0] = x->number;
    w(g, "~Mconst a_~I0 = [~N~+");

    for (int i = 0; i < x->literalstring_count; i++) {
        if (i) w(g, ",~N");
        g->I[0] = v[i].i;
        g->I[1] = v[i].result;

        w(g, "~M[");
        write_literal_string(g, v[i].b);
        w(g, ", ~I0, ~I1");
        if (v[i].function != NULL) {
            w(g, ", ");
            write_int(g, v[i].function_index);
        }
        w(g, "]");
    }
    w(g, "~N~-~M];~N~N");
}

static void generate_amongs(struct generator * g) {
    for (struct among * x = g->analyser->amongs; x; x = x->next) {
        generate_among_table(g, x);
    }
}

static void generate_among_dispatcher(struct generator * g, struct among * x) {
    if (x->function_count <= 1) return;

    struct amongvec * v = x->b;

    write_comment(g, x->node);

    g->I[0] = x->number;
    w(g, "~N~M/** @return {boolean} */~N");
    w(g, "~M#af_~I0() {~N~+");
    w(g, "~Mswitch (this.af) {~N~+");
    for (int n = 1; n <= x->function_count; n++) {
        w(g, "~Mcase ");
        write_int(g, n);
        w(g, ": return ");
        for (int i = 0; i < x->literalstring_count; i++) {
            if (v[i].function_index == n) {
                write_varref(g, v[i].function);
                w(g, "();~N");
                break;
            }
        }
    }
    w(g, "~-~M}~N");
    w(g, "~Mreturn false;~N");
    w(g, "~-~M}~N");
}

static void generate_among_dispatchers(struct generator * g) {
    for (struct among * x = g->analyser->amongs; x; x = x->next) {
        generate_among_dispatcher(g, x);
    }
}

static void set_bit(symbol * b, int i) { b[i/8] |= 1 << i%8; }

static void generate_grouping_table(struct generator * g, struct grouping * q) {
    int range = q->largest_ch - q->smallest_ch + 1;
    int size = (range + 7)/ 8;  /* assume 8 bits per symbol */
    symbol * b = q->b;
    symbol * map = create_b(size);

    for (int i = 0; i < size; i++) map[i] = 0;

    for (int i = 0; i < SIZE(b); i++) set_bit(map, b[i] - q->smallest_ch);

    w(g, "~Mconst /** Array<number> */ ");
    write_varname(g, q->name);
    write_string(g, " = [");
    for (int i = 0; i < size; i++) {
        if (i) w(g, ", ");
        write_int(g, map[i]);
    }
    w(g, "];~N~N");

    lose_b(map);
}

static void generate_groupings(struct generator * g) {
    for (struct grouping * q = g->analyser->groupings; q; q = q->next) {
        generate_grouping_table(g, q);
    }
}

static void generate_members(struct generator * g) {
    int wrote_members = false;

    for (struct name * q = g->analyser->names; q; q = q->next) {
        if (q->local_to) continue;
        switch (q->type) {
            case t_string:
                w(g, "~M#");
                write_varname(g, q);
                w(g, "/** string */ = '';~N");
                wrote_members = true;
                break;
            case t_integer:
                w(g, "~M#");
                write_varname(g, q);
                w(g, "/** number */ = 0;~N");
                wrote_members = true;
                break;
            case t_boolean:
                w(g, "~M#");
                write_varname(g, q);
                w(g, "/** boolean */ = false;~N");
                wrote_members = true;
                break;
        }
    }
    if (wrote_members) w(g, "~N");
}

static void generate_methods(struct generator * g) {
    for (struct node * p = g->analyser->program; p; p = p->right) {
        generate(g, p);
        g->unreachable = false;
    }
}

extern void generate_program_js(struct generator * g) {
    g->outbuf = str_new();
    g->failure_str = str_new();

    write_start_comment(g, "// ", NULL);

    // Disable some deno-lint warnings which the generated code can trigger.
    w(g, "// deno-lint-ignore-file"
         // Some of our generated deno-lint-ignore comments may not be used.
         " ban-unused-ignore"
         // Expressions in conditionals may be constant.
         " no-constant-condition"
         // Empty blocks may be generated in some cases.
         " no-empty"
         // Among var `a` is only assigned to once per `among`, but is declared
         // at the start of the function and may be initialised in a nested
         // block.
         //
         // Some localised variables may only be assigned to once.
         " prefer-const~N~N");

    generate_amongs(g);
    generate_groupings(g);

    generate_class_begin(g);

    generate_members(g);

    generate_among_dispatchers(g);

    generate_methods(g);

    generate_class_end(g);

    output_str(g->options->output_src, g->outbuf);
    str_delete(g->failure_str);
    str_delete(g->outbuf);
}
